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Abstract Previous meta‐analyses suggested that carnivorous plants—despite access to N, P, and K from prey—have significantly lower leaf concentrations of these nutrients than noncarnivores. Those studies, however, largely compared carnivores in nutrient‐poor habitats with noncarnivores in more nutrient‐rich sites, so that the differences reported might reflect habitat differences as much as differences in nutrient‐capture strategy. Here we examine three carnivorous and 12 noncarnivorous plants in the same nutrient‐poor bog to compare their foliar nutrient concentrations, assess their patterns of nutrient limitation using leaf NPK stoichiometry, and estimate percentage N derived from prey by carnivores using a mixing model for stable N isotopes. We hypothesized that (1) carnivore leaf nutrient concentrations approach or exceed those of noncarnivores in the same nutrient‐poor habitat; (2) species in different functional groups show different patterns of stoichiometry and apparent nutrient limitation; and (3) noncarnivores might show evidence of using other means of nutrient acquisition or conservation to reduce nutrient limitation. At Fallison Bog in northern Wisconsin, carnivorous plants (Drosera rotundifolia,Sarracenia purpurea,Utricularia macrorhiza) showed significantly lower leaf percentage C and N:P ratio, higher δ15N, and no difference from noncarnivores in leaf N, P, K, and δ13C. Sedges had significantly lower leaf percentage P, percentage C, and N:K ratio, and higher K:P ratio than nonsedges restricted to theSphagnummat, and may tap peat N via aerenchyma‐facilitated peat oxidation (oxipeditrophy). Evergreen ericaceous shrubs exhibited significantly higher levels of percentage C and lower values of δ15N than mat nonericads.Calla palustris—growing in the nutrient‐rich moat at the bog's upland edge—had very high values of leaf N, K, δ15N, and N:P ratio, suggesting that it may obtain nutrients from minerotrophic flows from the adjacent uplands and/or rapidly decaying peat. Stoichiometric analyses indicated that most species are N limited. A mixing model applied to δ15N values for carnivores, noncarnivores, and insects produced an estimate of 50% of leaf N derived from prey forUtricularia, 42% forSarracenia, and 41% forDrosera.
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To eat or not to eat: novel stable isotope models reveal a shift in carnivory with nutrient availability for aquatic Utricularia spp.
Abstract Background and AimsFreshwater nitrogen inputs are increasing globally, altering the structure and function of wetland ecosystems adapted to low nutrient conditions. Carnivorous wetland plants of the genus Utricularia are hypothesized to reduce their reliance on carnivory and increase their assimilation of environmental nutrients when the supply of ambient nutrients increases. Despite success in using stable isotope approaches to quantify carnivory of terrestrial carnivorous plants, quantifying carnivory of aquatic Utricularia requires improvement. MethodsWe developed stable isotope mixing models to quantify aquatic plant carnivory and used these models to measure dietary changes of three Utricularia species, Utricularia australis, U. gibba and U. uliginosa, in 11 wetlands across a 794-km gradient in eastern Australia. Diet was assessed using multiple models that compared variations in the natural-abundance nitrogen isotope composition (δ15N) of Utricularia spp. with that of non-carnivorous plants, and environmental and carnivorous nitrogen sources. Key ResultsCarnivory supplied 40–100 % of plant nitrogen. The lowest carnivory rates coincided with the highest availability of ammonium and dissolved organic carbon. ConclusionsOur findings suggest that Utricularia populations may adapt to high nutrient environments by shifting away from energetically costly carnivory. This has implications for species conservation as anthropogenic impacts continue to affect global wetland ecosystems.
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- Award ID(s):
- 1831075
- PAR ID:
- 10554989
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Annals of Botany
- Volume:
- 134
- Issue:
- 5
- ISSN:
- 0305-7364
- Format(s):
- Medium: X Size: p. 827-842
- Size(s):
- p. 827-842
- Sponsoring Org:
- National Science Foundation
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